Method of electrodepositing tin



Patented May 2, 1939 METHOD or ELECTRODEPOSITIING TIN Jehu P. Cooper,Woodbridge, and Donald Willis Light, Perth Amboy, N.

J., assignors to Inter- I national smelting and Refining Company, PerthAmboy, N. a corporation of Montana g No Drawini.

17 Claims.

This invention relates to the electrodeposition of tin, and has for itsprincipal object'the provision of an improved electrolytic method fordepositing tin in metallic form. More especially, the invention providesan improved electrolyte for use in conjunction tion of tin] Inaccordancewith the invention, an anode containing tin is subjectedto'anelectrolytic operation in the presence of an electrolyte comprising atar acid and pyroligneous acid. Cresylic acid is a particularlysatisfactory tar acid for use in the electrolyte. In addition to the taracid and pyroligneous acid, which generally are employed in theproportions of one to two, the electrolyte usually contains a mineralacid such as sulphuric acid, and dissolved tin. One or more additionagents such as glue or goulac may also be included in the electrolyte.

' In carrying out the invention, tin-containing anodes are suitablyprepared and introduced into an electrolytic cell in contact with anelectrolyte containing a tar acid and pyroligneous acid. Cathodes(starting sheets) of substantially pure tin are prepared and introducedinto the cell in contact with the electrolyte, and an electric currentis passed from the anode through the electrolyte to the cathode, therebyefiecting disclution of tin from the anode and deposition ofsubstantially pure tin at the cathode. I

' The electrolyte employed in carrying out the invention comprises, inaddition to the tar acid and pyroligneous acid, anaqueous solution ofsulphuric acid. The tar acid and pyroligneous acid advantageously areemployed in the electrolyte in the proportions of one to two, withenough sulphuric acid to bring the total acid content of the electrolyteto about 125 grams per liter, calculated as H2804.

Most of the commercially available tar acids may be used in preparing,the electrolyte. The xylenol fraction of tar acid, composed principallyof xylenol, may be employed with success, but at present the cresolfraction, composed principally of cresylic acid, is preferred.Commercial cresylic acid of course is not a pure cresol or a mixture ofpure cresols-it contains small amounts of both higher and lowerhomologues of cresol. The term cresylic acid as used in thisspecification refers particularly to commercially available cresols andis' not intended to cover only pure cresols, although it does notexclude them. A

concentration of about 6 grams per liter of cre- 4 sylic acid in theelectrolyte is quite satisfactory.

Commercial pyroligneous acid, recovered durwith the electrolytic deposi-Application January 11, 1937, Serial'No. 120,036

ingthe destructive distillation of wood, is employed in the electrolyte.-Pyroligneous acid is composed of an aqueous mixture of methyl alcohol(about 1-2%) acetic acid (about 10%), acetone (about 0.1-0.5%) andvarious other organic acids, esters and alcohols in small quantities.

About twice as much pyroligneous acid ascresylic acid is used in theelectrolyte, a concentration of about 12 grams per liter of pyroligneousacid being satisfactory.

Sulphuric acid is employed in the electrolyte in a concentration ofabout 110 to about 115 grams per liter. Dissolved tin is present in theelectrolyte, principally in the stannous form and advantageously in aconcentration of about 20 to 35 grams per liter, although lowerconcentrations than 20 grams per liter have been employed successfully.

In addition to the above reagents, the electrolyte may contain smallamounts of such addition agents as glue and goulac.

At present the invention is employed successfully in refining impuretin. Impure anodes containing tinand substantially pure tin cathodes, orstarting sheets, are placed in a suitable electrolytic cell in contactwith an electrolyte, such as described above, containing about 6 gramsper liter of cresylic acid, about 12 grams per liter of pyroligneousacid, about 110 to 115 grams per literof sulphuric acid, about 20 to 35grams per liter of dissolved tin, and a small quantityof glue.

The electrolysis is carried out with a cell voltage of about 0.3 to 1.0and a current density of about 5 amperes per square foot of anodesurface. Tin is dissolved from the anode, and tin is deposited insubstantially pure form at the cathode. There is amarked tendency forthe electrolyte to become depleted in tin during the course of theelectrolysis, and the electrolyte is therefore withdrawn from the cell,circulated over metallic tin, advantageously in the form of pellets, orshot tin, and returned to the cell. During this circulation metallic tinis dissolved by the electrolyte to maintain therein a proper tinconcentration, preferably above about 20 grams per liter.

In employing the method of the invention in the above-described manner,reagents "in the electrolyte are consumed, probably in part by occlusionon the cathodic deposit and in part by inclusion in the slimes, whichare withdrawn from the cell. This consumption, on the basis of one tonof deposited cathode tin, amounts to about 15 pounds of cresylic acid,about 30 pounds of pyroligneous acid, and about 5 pounds of glue. Somesulphuric acid also is lost during the electrolysis, but its amount isnegligible. Appropriate additions 01 these reagents are made to theelectrolyte to maintain a proper electrolyte composition. Such additionsmay be made to the electrolyte in the cell, or better to the electrolytein the course of its circulation outside the cell, either continuouslyor intermittently.

The invention described above has been found to give excellent results.Growths or trees sprouting from the cathode, which have always been aproblem in the electrolysis of tin, do not occur to any substantialextent when employing the method of the invention. The currentefficiency of a cell operating in accordance with the invention is inthe neighborhood of 90% and more, substantially higher than in mostprocesses for the electro-refining of tin. The tin cathodes runsubstantially above 99% tin, and are of a fine crystalline texturerendering them easy to work with.

Heretofore known processes for depositing tin electrolytically have madeuse of electrolytes containing either pyroligneous acid or cresylic acidalone, but suchprocesses do not lead to as satisfactory results as thosesecured in accordance with the invention, in which pyroligneous acid anda tar acid are employed together in the electrolyte. Although formerlyit was thought that pyroligneous acid and tar acids served substantiallythe same purpose in the electrolyte, it has been found that togetherthey exert an influence of which neither one alone is capable. The ex-'act mechanisms by which these two reagents operate conjointly is notfully understood; it is not possible, however, to replace one with theother, nor to secure the results of the invention by the use of eitherone alone, irrespective of the amount in which it is used.

We claim:

1. In the electrodeposition of tin, the improvement which comprisesobtaining electrolytically deposited tin of fine crystalline texture andsubstantially free of growths or' trees" by subjecting ment whichcomprises obtaining electrolytically deposited tin of fine crystallinetexture and substantially free of growths or trees by subjecting ananode containing tin to electrolysis in an aqueous electrolytecomprising cresylic acid, pyroligneous acid, and sulphuric acid.

4. In the electrodeposition of tin, the improvement which comprisesobtaining electrolytically deposited tin of fine crystallinetexture andsubstantially free of growths or "trees" by subjecting an anodecontaining tin to electrolysis in an aqueous electrolyte comprisingcresylic acid, pyroligneous acid, sulphuric acid, and dissolved tin.

5. In the electrodeposition of tin, the improvement which comprisesobtaining electrolytically deposited tin of fine crystalline texture andsubstantially free of growths or "trees by subjecting an anodecontaining tin to electrolysis in an aqueous electrolyte comprising atar acid, about 12 grams per liter of pyroligneous acid, and a mineralacid.

6. In the electrodeposition oi tin, the improvement which comprisesobtaining electrolytically deposited tin of flne crystalline texture andsubstantially free of growths or "trees" bysubjecting an anodecontaining tin to electrolysis in an aqueous electrolyte comprisingpyroligneous acid, about 6 grams per liter of cresylic acid, and amineral acid.

7. In the electrodeposition of tin, the improvement which comprisesobtaining electrolytically deposited tin of fine crystalline texture andsubstantially free of growths or trees by subjecting an anode containingtin to electrolysis in an aqueous electrolyte comprising about 6 gramsper liter cresylic acid, about '12 grams per liter of pyroligneous acid,and a mineral acid.

8. In the electrodeposition of tin, the improvement which comprisesobtaining electrolytically deposited tin of fine crystalline texture andsubstantially free of growths or trees by subject ing an anodecontaining tin to electrolysis in an aqueous electrolyte comprisingcresylic acid, pyroligneous acid, and about 110 to 115 grams per literof sulphuric acid.

.9. In the electrodeposition of'tin, the improvement which comprisesobtaining electrolytically deposited tin of fine crystalline texture andsubstantially free, of growths or trees by subjecting an anodecontaining tin to electrolysis in an aqueous electrolyte comprisingcresylic acid, pyroligneous acid and sulphuric acids in proportions suchthat the total acids in the electrolyte amount to about 125. grams asH2804.

10. In the electrodeposition of tin, the improvement which comprisesobtainingelectrolytically deposited tin of fine crystalline texture andsubper liter, calculated stantially free of growths or trees bysubje'cting. an anode containing tin to electrolysis in an aqueouselectrolyte comprising about 6 grams per. liter of cresylic acid, about12 grams per liter of pyroligneous acid,'and about 110 to 115 grams perliter of sulphuric acid.

11. In the electrodeposition of tin, the iniprovement which comprisesobtaining electro lytically deposited tin of line crystalline textureand. substantially free of growths or trees by subjecting an anodecontaining tin to electrolysis in an aqueous electrolyte comprising atar acid, pyroligneous acid, a mineral acid, and about 20 to 35 gramsper liter of dissolved tin.

12. In the electrodeposition of tin; the improvement which comprisesobtaining electrolytically deposited tin of fine crystalline texture andsubstantially free of growths or trees by subjecting an anode containingtin to electrolysis in an aqueous electrolyte comprising cresylic -acid,pyroligneous acid, a mineral acid, and

about 20 to 35 grams per liter of dissolved tin.

13. In the electrodeposition of tin, the improvement which comprisesobtaining electrolytically deposited tin of fine crystalline texture andsubstantially free of growths or trees by subjecting an anode containingtin to electrolysis in an aqueous electrolyte comprising tar acid andpyroiigneous acid in the proportion of about one to two; and a mineralacid.

14: In the electrodeposition of tin, the improvement which comprisesobtaining'electrolytically deposited tin of fine crystalline textureand'substantially free of growths or trees by subjecting an anodecontaining tin toelectrolysis in an aqueous electrolyte comprisingcresylic acid and pyroligneous acid in the proportion of about one totwo, and a mineral acid.

15. In the electrodeposition of tin, the improvement which comprisesobtaining electrolytically deposited tin of fine crystalline texture andsubstantially free of growths or trees by subjecting an anode containingtin to electrolysis in an aqueous electrolyte comprising a tar acid,pyroligneous acid, a mineral acid, and glue.

16. In the electrodepositlon of tin, the improvement which comprisesobtaining electrolytically deposited tin of fine crystalline texture andsubstantially free of growths or trees by subjecting an anode containingtin to electrolysis in an aqueous electrolyte comprising a tar acid,pyroligneous acid, a mineral acid, and dissolved tin, and circulatingthe electrolyte in contact with metallic tin to avoid depletion of theelectrolyte in tin.

17. In the electrodeposition of tin, the improvement which comprisesobtaining electrolytically deposited tin of fine crystalline texture andsubstantially free of growths or trees by subjecting an anode containingtin to electrolysis in an aqueous electrolyte comprising cresylic acid,pyroligneous acid, a mineral acid, and about 20 to 35 grams per liter ofdissolved tin, and circulating the electrolyte in contact with metallictin to maintain the concentration of dissolved tin above about 20 gramsper liter.

JEHU P. COOPER. DONALD WILLIS LIGHT.

